1. Field of the Invention
The present invention relates to an apparatus used for preventing an image blur of an optical equipment such as a camera.
2. Related Background Art
FIG. 9 shows a conventional image blur prevention system for preventing an image blur of a camera.
In the arrangement shown in FIG. 9, the output from a fluctuation (vibration) sensor 500 for detecting the hand vibration amount of the entire camera by a photographer is input to a filter circuit 501 so that an unnecessary DC component or the like is removed from the output from the sensor 500. Then, the output from the filter circuit 501 is input to a sample hold circuit 502. The sample hold circuit 502 samples the input signal at a predetermined time interval in synchronism with timing signals T generated at a predetermined time interval from a timing signal generation means 506, and transfers its output to an A/D converter 503.
Subsequently, the A/D converter 503 executes an A/D conversion operation of the input signal in synchronism with timing signals at the predetermined time interval, which are similar to the above-mentioned signals, and a calculation means 504 converts the digital data into driving data for driving a correction system (optical correction by driving a lens, image correction for changing the extraction timing of, e.g., a CCD, or the like) for correcting an actual fluctuation, on the basis of a predetermined calculation operation (to be described later).
The conversion result is converted into analog data again by a D/A converter 505, and electrical power corresponding to the level value of this analog signal is supplied to a correction system 508 via an electrical power amplification circuit 507 (which is not necessary in the case of image correction), thus driving the correction system. Note that the constituting means 502 to 506 surrounded by a dotted line can be normally realized by a single CPU.
As described above, the fluctuation sensor output (including the output from the correction system when the correction system is feedback-controlled) is sampled and A/D-converted at a predetermined time interval, calculation control is performed based on the digital data, and driving data are output at a predetermined time interval.
However, the conventional method must satisfy t.sub.1 +t.sub.2 .ltoreq.T (where T is the sampling time interval, t.sub.1 is the conversion time of the A/D converter, and t.sub.2 is the calculation time). Since these times t.sub.1 and t.sub.2 are normally limited by the performance of a CPU, it is impossible to shorten the sampling time interval to be smaller than a certain time period.
In general, when the maximum frequency of an input signal is represented by f.sub.max, a signal component having a frequency different from that of an original frequency component is generated in the sampling result (sampling theorem) unless the sampling time interval T is equal to or smaller than: ##EQU1## For this reason, the upper limit value of T is undesirably limited to some extent. In the case of normal image blur prevention control, the sampling time interval is about 1 to 2 kHz in terms of frequency in consideration of the calculation performance of a normal microcomputer. In this case, a normal hand vibration signal has several ten Hz, while the fluctuation sensor may generate a signal of several kHz (for example, when a fluctuation gyro is used as a fluctuation sensor, a resonance frequency component between a vibration member and a support base appears) due to, e.g., a mechanical shock generated by the movement of a quick return mirror, travelling of a shutter, and the like of a single-lens reflex camera. When this signal is sampled at a normal sampling time interval, the original signal cannot often be reproduced.
FIGS. 10A and 10B show this state. FIG. 10A shows an actual fluctuation signal, and FIG. 10B shows the sampling/hold result of the signal shown in FIG. 10A at the sampling time interval T. As can be seen from this waveform, in the sampling/hold result shown in FIG. 10B, high-frequency components such as a shock are not detected at all and the original hand vibration signal cannot be detected, either.